Apache Hadoop's LinuxContainerExecutor runs docker commands as root with insufficient input validation

In Apache Hadoop 2.8.0, 3.0.0-alpha1, and 3.0.0-alpha2, the LinuxContainerExecutor runs docker commands as root with insufficient input validation. When the docker feature is enabled, authenticated users can run commands as root. This issue is fixed in versions 2.8.1 and 3.0.0-alpha3.